This invention relates generally to improvements in medication-containing syringes and related infusion pumps for controlled delivery of a selected medication from the syringe to a patient. More particularly, this invention relates to an improved syringe plunger adapted for direct drive connection with the infusion pump is a manner assuring proper interengagement between the syringe and pump.
Infusion pump devices and systems are relatively well known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact housing adapted to receive and support a syringe carrying the prescribed medication for administration to the patient through infusion tubing and an associated catheter or the like. The infusion pump includes a small drive motor connected via a lead screw assembly for motor-driven advancement of a syringe piston plunger to deliver the medication to the patient. Programmable control means can be provided for operating the drive motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of medication over an extended period of time. Such infusion pumps are utilized to administer insulin and other medications, with exemplary pump constructions being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653; 5,097,122; and 5,505,709, which are incorporated by reference herein.
Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication over an extended period of time. The infusion pump is often designed to be extremely compact and thus may be adapted to be carried by the patient, for example, by means of a belt clip of the like. As a result, important medication can be administered with precision and in an automated manner, without significant restriction on the patient's mobility or lifestyle.
To achieve accurate and reliable delivery of medication to the patient in response to motor-driven advancement of the syringe piston plunger, it can be extremely important to use a syringe designed to meet a narrow set of operational specifications which are compatible with the syringe pump. That is, variations in the size and shape of the syringe, friction forces attributable to sliding plunger seals, etc., can result in significant variations in the amount of medication delivered in response to operation of the pump drive motor. Moreover, the mechanical coupling between the pump lead screw and the syringe plunger, typically to include a lead screw nut and related latch mechanism for engaging a flange or the like on the syringe plunger, can inherently include a small degree of lost motion or backlash which can also result in significant variations in the medication delivery volumes. In addition, incorrect installation of the syringe into the infusion pump housing can cause inaccurate delivery or nondelivery of the medication to the patient.
In the past, modified medication infusion pumps and related syringes have been proposed with a direct drive connection between the syringe plunger and a pump lead screw, in attempts to provide medication delivery with improved precision. See, for example, U.S. Pat. No. 4,648,872 and PCT WO 96/14893. In these proposals, the syringe plunger is equipped with a threaded element for engaging the pump lead screw, and a movable door or cover functions when closed to engage and hold the syringe in a position with the threaded element engaging the lead screw. While these designs provide the desired direct drive connection, they are dependent upon proper retention of the door or cover in the closed position to obtain proper medication delivery. If the door or cover becomes slightly ajar, the threaded element can become partially or completely disengaged from the lead screw, resulting in inaccurate partial delivery or nondelivery of the medication.
The present invention overcomes these problems and disadvantages by providing an improved syringe and related medication infusion pump, wherein the syringe plunger includes a threaded element adapted for secure direct drive coupling with a lead screw independent of the open or closed position of an infusion pump door or cover. However, in the event that the syringe plunger is not properly connected to the lead screw, an associated door or cover on the infusion pump cannot be closed thereby alerting the patient to such improper engagement.